Adenovirus-mediated manganese superoxide dismutase gene transfer to hamster cheek pouch carcinoma cells

As a first step in evaluating the tumor suppressor activity of the manganese superoxide dismutase (MnSOD) gene on established tumors in vivo, we used adenovirus-mediated gene transfer as a means of delivering the MnSOD cDNA to hamster cheek pouch carcinoma (HCPC-1) cells in vitro. HCPC-1 cells were transduced with the adenovirus-MnSOD construct (AdMnSOD) at multiplicities of infectivity (MOI) of 0, 10, 25, 50, 100, 150, and 200 MOI or with the adenovirus-LacZ reporter gene construct (AdLacZ) at 100 MOI. Dose-dependent increases in MnSOD immunoreactivity were seen on Western blotting and indirect immunofluorescence microscopy with increasing AdMnSOD titers. Maximal immunoreactivity was observed at 100 MOI AdMnSOD with both techniques. Moreover, we observed a concomitant 6-7-fold increase in MnSOD activity compared with parental cell levels that also peaked at 100 MOI AdMnSOD. To determine the effect of transgene-expressed MnSOD on tumor cell behavior, we examined cell growth, plating efficiency, and anchorage- dependent growth in soft agar. Cell number measured on day 13 decreased approximately 50% with 100 MOI AdMnSOD (P < 0.05) compared with parental cells. Moreover, cell doubling time increased from 38 to 44 h with 100 MOI AdMnSOD. Plating efficiency and cell growth in soft agar decreased approximately two-thirds with 100 MOI AdMnSOD (P < 0.001). These assays of the transformed phenotype in vitro all appeared to show maximal effect with 100 MOI AdMnSOD. As tumor growth in vivo is most predictable by a combination of these in vitro data, our results suggest that if MnSOD can be effectively delivered to a tumor in vivo using the adenovirus paradigm, effective tumor growth suppression can be observed.